Asking questions is how we learn and what forums are for
For cracking your skull: After either winning the civil war or failing to talk Briony out of her terrible idea at the birthday party, participate in the tournament you host. When Kevin gets upset with you, choose to fight him with staves while having little to no pole-arm skills.
For exploding: Attempt to sink the invading fleet with magic, while having a very low wield magic skill. It's easier to blow yourself up if you have only two other Lumens with you (your mentor plus one of the two secret Lumens you can uncover; don't find both!).